1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a silicon single crystal which is manufactured by pulling up a silicon single crystal by the Czochralski method (the CZ method), and to a silicon single crystal which is manufactured by using this apparatus or method.
2. Background Art
A silicon single crystal is manufactured by heating up a polycrystalline silicon raw material filled in a crucible using a heater to obtain a molten silicon, and pulling up a silicon single crystal from the molten silicon to grow by the CZ method. A silicon wafer is manufactured by slicing (cutting) the silicon single crystal which is manufactured by the above described method, and integrated circuits is formed on the silicon wafer. Considering a formation of the integrated circuits on the silicon wafer, it is desirable that the silicon wafer has a high quality in which the number of COPs (Crystal Originated Particles) exerting an influence on a gate oxide integrity of the silicon wafer is small. It is well known that COPs occur inside OSF (Oxidation Induced Stacking Fault) rings and dislocation clusters and the like occur when a pulling rate is reduced. Furthermore, it is also known that a distribution of these defects depends on a value (V/G) which is a ratio of the pulling rate V of the silicon single crystal and a temperature gradient G in a vertical direction in a vicinity of a solid-liquid interface of the silicon single crystal. That is to say, it is necessary to keep the value of V/G within a predetermined range in order to manufacture a single crystal in which the number of COPs is low (largely depends on a distribution of defects) with a stabile quality.
However, since the temperature gradient G changes due to various factors in a mass production of the silicon single crystals, in the case in which the silicon single crystal is pulled up at a constant pulling rate V, the value of V/G varies, and as a result, the product quality of the silicon single crystals varies widely. In the following Patent documents 1 and 2, methods for manufacturing silicon single crystals having no defects in which a temperature gradient of the silicon single crystal in a lengthwise direction (a vertical direction) is measured using a non contact temperature sensor, and a pulling rate for the silicon single crystal is controlled based on the measured temperature gradient so as to keep the value of V/G within a predetermined range.
However in the above described prior art, the measurement values measured by the temperature sensor varies greatly, depending on a position of the temperature sensor with respect to the silicon single crystal which is pulled out. Accordingly, it is necessary to adjust the position of the temperature sensor precisely for each production batch, and a lot of work and time are required for arranging and managing the temperature sensor. Here, the production batch means a whole set of processes performed to manufacture one silicon single crystal. Since a large number of apparatuses for manufacturing silicon single crystals are provided in a factory for silicon single crystals, in the case in which temperature sensors are employed for each of them, there is a problem in which a lot of work is required. Also, there is a problem in which a cost of the apparatus for manufacturing the silicon single crystal is increased by the provision of the temperature sensor. Furthermore, there is also a problem that, in the case in which the temperature sensor is provided in the apparatus for manufacturing silicon single crystals, a working efficiency of doing maintenance in an interior of the apparatus (for example, changing carbon members in a furnace and the like) is deteriorated. Due to the above considerations, it would be desirable to keep the value of V/G within the predetermined range by some method other than the method of controlling the pulling rate based on the measurement values measured by the temperature sensor.
Patent document 1 Japanese Unexamined Patent Application, First Publication No. 2000-143388.
Patent document 2 Japanese Unexamined Patent Application, First Publication No. 2001-220285.